This application is based on Patent Application No. 2000-285367 filed Sep. 20, 2000 in Japan, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an ink jet printing apparatus that ejects ink for printing, to a method of supplying ink and to a method of recovering an ink jet print head. More particularly, the present invention relates to an ink jet printing apparatus having an ink supply device for supplying ink to the ink ejecting print head, to a method of supplying ink for the ink jet printing apparatus and to a method of recovering the print head thereof.
2. Description of the Related Art
Heretofore, an ink jet printing apparatus that prints on a print medium by ejecting ink has the advantages of being very silent during operation, small in size and inexpensive and thus have found recently a wide range of applications. An ink jet print head used in such an ink jet printing apparatus to eject ink onto a print medium for printing are classed into two types: one that uses a piezoelectric element and the other, called a bubble jet type, which uses an electrothermal transducer to cause a film boiling in ink and eject ink by a force of a generated bubble.
A known method for supplying ink to the print head involves installing on a carriage a sub tank capable of accommodating a small amount of ink and supplying ink to the sub tank from a main ink tank. This method can increase the carriage speed and is thus suited for high-speed printing. In addition, because the main tank can have a large capacity, this method is advantageously applied for a large volume printing. There are many constructions proposed for such an ink supply method. Among them is a pit-in type in which during a non-printing period the sub tank is automatically refilled by a large-capacity main ink tank set at an arbitrary location in the ink jet printing apparatus. Another example construction for such a method has the main ink tank installed at other than the carriage of the ink jet printing apparatus and supplies ink from the main ink tank to the sub tank through a tube. In these printing apparatus, the sub tank has a function of temporarily holding bubbles when air entering the ink emerges as bubbles and thereby minimizing adverse effects on printing.
As the percentage of the bubbles in the sub tank increases, there is a possibility that, due to environmental changes such as temperature variations at a location of the printing apparatus, the bubble may expand and cause the ink to leak out of the print head.
To deal with this problem a variety of methods have been proposed to reduce or eliminate the bubbles remaining in the sub ink tank. For example, one method deaerates the ink contained in the main ink tank. This method requires a step of deaeration and must hermetically enclose the ink tank during transport or in use. Another method of eliminating bubbles in the sub ink tank comparatively reduces the volume of the sub ink tank and eliminates the ink and the bubble from the sub ink tank at the same time by suction. This method, however, increases the amount of discarded ink. Further, if the amount of bubbles, i.e., the amount of ink, in the sub ink tank is not known, the number of recovery operations and therefore the amount of discarded ink tend to increase making it necessary to check the amount of remaining ink in the sub ink tank.
The present invention has been accomplished to solve the above-described problems and it is therefore an object of the present invention to provide an ink jet printing apparatus with a main tank and a sub tank, a method of supplying ink and a method of recovering an ink jet print head, which offer a simple construction and can reliably eliminate bubbles while minimizing the amount of discarded ink even when the amount of bubbles in the sub tank is not clearly known.
To achieve the above objective, the ink jet printing apparatus of the present invention comprises; an ink jet print head for ejecting ink, a sub ink tank for temporarily holding the ink to be ejected from the print head, a main ink tank for holding the ink to be supplied to the sub ink tank, and an ink moving means for returning almost all of the ink in the sub ink tank to the main ink tank.
The method of supplying ink of the present invention is used for the ink jet printing apparatus, wherein the ink jet printing apparatus comprises an ink jet print head for ejecting ink, a sub ink tank for temporarily holding the ink to be ejected from the print head, and a main ink tank for holding the ink to be supplied to the sub ink tank, the method of supplying ink comprises; a first step of returning the ink in the sub ink tank to the main ink tank, a second step of discharging bubbles in the sub ink tank out of the sub ink tank, and a third step of, after the first step, supplying a predetermined amount of ink from the main ink tank to the sub ink tank.
The method of recovering the ink jet print head of the present invention is used for the ink jet printing apparatus with an ink supply path, and the method of recovering the ink jet print head comprises, a first step of returning the ink in the sub ink tank to the main ink tank, and a second step of discharging the ink from the print head by, after the first step, applying an external pressure against any part of the ink supply path.
With the ink jet printing apparatus, the method of supply ink and the method of recovering the ink jet print head according to the present invention, because the ink in the sub ink tank is returned to the main ink tank and because the amount of ink to be supplied from the main ink tank to the sub ink tank is known, the ink can be prevented from overflowing from the sub ink tank when the recovery operation is performed. A predetermined amount of ink can be injected into the sub ink tank during the recovery operation.
Further, in the ink jet printing apparatus of the present invention, the ink jet print chip having energy generating elements for ejecting ink and a nozzle portion for ejecting ink may be arranged on one of surfaces of the sub ink tank. This construction offers an advantage, in addition to those described above, of being able to appropriately restore the nozzle portion from clogging.
Further, in the ink jet printing apparatus of the present invention, the main ink tank and the sub ink tank for storing ink may be connected together through a tube. This construction offers an advantage, in addition to those described above, of being able to restore the nozzle portion from clogging with a small amount of discarded ink.
Further, in the ink jet printing apparatus of the present invention, the main ink tank for storing ink may be arranged at a height lower than the ink jet print head. In that case, there is an advantage, in addition to those described above, that the positional difference between the main ink tank and the ink jet print head can be utilized as an attitude difference appropriately in returning the ink to the main ink tank during the recovery operation.
Further, in the ink jet printing apparatus of the present invention, the sub ink tank may have a valve to communicate the interior of the sub ink tank to the external air. By using the positional difference between the sub ink tank and the main ink tank, the external air can easily be taken into the sub ink tank, contributing to the proper discharging of the ink out of the sub ink tank.
Further, in the ink jet printing apparatus of the present invention, the means for discharging the ink out of the sub ink tank may be one that deforms the sub ink tank. In that case, because the ink can be discharged properly as the sub ink tank is deformed, the clogging of the nozzle portion can be eliminated with a small amount of discarded ink.
Further, in the ink jet printing apparatus of the present invention, because the supply of ink to the sub ink tank is done by the pit-in system that connects the sub ink tank to the main ink tank when necessary, it is possible to easily and properly replace the sub ink tank.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.